An encoder circuit and A/D converter that can minimize the error of an encoder output with respect to all the possible combinations of thermometer codes are desired to be provided. To this end, an encoder circuit has a logic thereof configured to take a thermometer code as an input and to output as an encoded value a center value of a range in which one or more encoded values are distributed, the one or more encoded values corresponding to positions of one or more boundaries between "0" and "1" appearing in the thermometer code.